Photographic exposure calculator



Dec. 29, 1942.

H. P. ROCKWELL, JR

FHOTOGRAPHIC EXPOSURE CALCULATOR Original Filed April 24, 1939 7m a SURE 'HME (sno ATTORNEYS Patented Dec. 29, 1942 UNITED STATES PATENT OFFICE 2,306,641 PHOTOGRAPHIO EXPOSURE CALCULATOR llarveyB. Rockwell, Jr., East Orange, N. 3., assi'gnor to Weston Electrical Instrument Corporation,.a corporation of New Jersey Original application April 24, 1939, Serial No.

269,762. Divided and this application February 19, 1941, Serial No. 379,721

3 Claims. (Cl. 235-88) -This application is a divisionoi my copending application, Serial No. 269,762, filed April 24, 1939, now matured into Patent No. 2,235,590, and relates to the calculator disclosed but not claimed in the patent.

in the patent just referred to there is described a system for making prints or transparencies from photographic positive or negative transparencies. As stated in the patent, photographic negatives vary irom one another in the diflerences between maximum density and minimum density, and also vary from one another in the absolute values of their densities, and therefore much time and material are ordinarily wasted in selecting the proper grade of paper to use, and in determining the proper amount of exposure to give, when making prints from the negatives. The system described in the patent .is intended to save the time and material which give an understanding of the meaning of the values placed upn the calculator and how they are determined the complete system disclosed in the patent wlllbe briefly described.

It includes a determination by means of a densitometer of the maximum and minimum densities of the negative. It also includes a determination, by means of a light meter, of the illumination produced by the printing light at the location to be occupied by the paper. The system further includes a determination, either by the manufacturer of the paper or by the person doing the printing, of the paper range of various types of papers, i. e., the increments of exposure necessary in the case of each type of paper to proceed from the lightest useful gray to the darkest useful black, and then a grading of the papers-according to the different paper ranges so determined. Each grade of paper is tested for its sensitivity either by the manufacturer, or the person making the prints, and the sensitivity of each grade of paper is noted either lay marking it on all pieces of paper of that grade, or on the package containing papers of that grade, or upon a suitable chart.

The values thus obtained are correlated on the calculator so that with a knowledge of the minimum and maximum densities of a particular negative from which a print is to be made,

.- the illumination of the printing light, and the sensitivity of any grade of paper which the cal culator may denote for use with that negative, the calculator may be manipulated as hereinafter described to denote the proper grade of paper to be used and to indicate the exposure time in seconds that should be given when that particular paper is used with the particular negative. The person making the print is thus relieved of the necessityof making the various time consuming estimates which would ordinarily be necessary.

The calculator is illustrated in the accompany.- ing drawing. preferably in the form of a disc, and two additional discs M and 42 rotatably mounted on the disc ltl and rotatable relative to each other. A part of the surface of the bottom disc- Ml is laid off in equal radial divisions 43, and in each of I these divisions is placed one of a series of numbers which correspond to the negative densities. In the drawing this series of numbers is designated Negative density. It will be noted that the numbers forming the series are uniformly spaced around a portion of the arc of a circle on the disc fill. A part of the remainder of the surface of this disc is divided into similar equal radial divisions M and in each of these divisions is placed one of a series of numbers representing different exposure times (in seconds) which may be given when making a print. In the drawing this series of numbers is designated Exposure time (seconds)." These numbers, it will he noted, are spaced around a part of the unused portion of the above mentioned circle on disc it. The top disc 32 has one portion whose radius is substantially equal to the radius of the said circle and another port-ion whose radius is less than the radius of the circle, as shown in the drawing. The top disc 42 is also-laid off in similar equal radial divisions '(equal to one another and angularly equal to the other divisions 43 and M) and these divisions contain the same numbers as those in divisions 43, but they proceed around the arc in the opposite direction. This series is designated in the drawing as Paper range. The numbers in this series, as will be seen from the drawing, are uniformly spaced around the outermost edge of the disc 32, i. e., around the edge of that portion of the disc whose radius is substantially equal to the radius of the It comprises a bottom member l8 .mentioned patent.

above mentioned circle on disc 40. The disc 42 also contains an indicator 46 at one point of the outermost edge of this disc. This indicator is preferably positioned next to the number .1 on disc 42. Because the disc 42 is rotatable with respect to the disc 40 this indicator may be set in registration with any desired density number of the disc 40. If it is set opposite the density number corresponding to the maximum density indicated by the meter of the densitometer for a particular negative, the density difference of the negative will be shown on the disc 42 opposite the number on disc 40 which corresponds to the minimum density indicated by the meter of the densitometer for that negative, This density difference corresponds to the paper range and is a number which indicates the grade of paper to be used in printing from the particular negative.

The intermediate disc 4| has a radius greater than the smallest radius of the' disc 42, but 'not greater than the radius of the above mentioned circle on disc 40. The edge portion of this disc is laid off in equal radial divisions, similar to the radial divisions on the other discs, and bears two sets of numbers 41 and 48 on arcs of different radius. The numbers 41 represent the sensitivities of various grades of paper, the values being determined by the system described in the above These numbers are designated Paper speed value in the drawing. The numbers 41 arearranged on the disc 4| around an arc having a radius less than the minimum radius of the disc 42. Thus they lie under a portion of the disc 42 except where a window 49 occurs in that disc. This window is provided so that only one of the paper speed numbers is exposed to view at a particular time.

The numbers 48 on the intermediate disc 4|, or at least a useful portion thereof, are not obsoured by the top disc 42. They are arranged around the edge portion of disc 4| so that they will cooperate with the exposure time numbers 44 on the disc 40. The numbers 48 represent various intensities of illumination produced by the printing light as measured in accordance with the system described in said patent. These numbers are designated Illumination in the draw- In using the calculator the operator sets the indicator 46 at that one of the negative density numbers on disc 40 which corresponds to the reading of the meter of the densitometer when the negative was tested for its maximum density. For instance, if the meter read 2.4 when the negative was tested for its maximum density, the top disc 42 will be turned until the indicatcr 46 points ,to 2.4 on disc 40, as shown in the drawing. The

if operator then observes on radial divisions 45 the number which registers with that one of the numbers on the disc 40 which corresponds with the minimum density of the negative, as determined by the operator when he tested the negative for its minimum density. For example, if the minimum density of the tested negative is .7 the operator observes from radial divisions 45 that the registering number in these divisions is 1.7. In accordance with the system of grading papers described in the above mentioned patent, this number will'denote the grade of paper which will reproduce the full range of the negative and will use the full useful tone range of the paper in so doing. The operatonleaves disc 42 where it is but moves disc 4| until there appears in window 49 that one of the paper speed values which represents the sensitivity of the denoted grade of paper. As above stated, each grade of paper has been tested for its sensitivity and has been assigned a paper speed value so the operator will know, for instance, by 'a suitable marking on the grade of paper, or its container, or by reference to a chart, that a particular one of the paper speed values 41 corresponds to the particular grade of paper that has been denoted by the calculator, and he will adjust the position of disc 4| until that paper speed value makes its appearance in the window 49. The operator now reads from disc 40 the number appearing in that one of divisions 44 which registers with that one of the illumination numbers 48 which was indicated by the light meter when the illumination of the printing light was measured. This number on disc 40 is the number of seconds exposure which the operator must give with the particular negative and with that particular printing light in order to secure a proper print'on the particular paper denoted by the calculator.

The term negative is used herein to refer to the transparency from which reproduction is to be made, regardless of whether the transparency is really positive or negative in character, and the term print is used to refer to the reproduction. Even though reference has been made to a paper print, it will be understood that the print may be a transparency.

I claim:

1. A calculator for use in determining the proper photographic paper to use and the proper exposure time to be given in order satisfactorily to print from a negative which consists of a surface, numbers corresponding to the densities of the photographic negatives uniformly spaced around a portion of the arc of a circle on said surface, a disc a portion of which has a radius equal to the radius of said circle and another portion of which has a radius less than the radius of said circle, said disc being rotatably mounted about its center concentrically with said circle, an indicator at one point of the outermost edge of said disc, numbers on said disc corresponding to the numbers on said surface, said numbers being uniformly spaced from said indicator around the outermost edge of said disc and in the same direction as the numbers around the arc of said circle but in the reverse order so that when said indicator is set opposite the number on said surface corresponding to the maximum density of the negative 9, number indicative of the-type of photographic paper that will record the density range of the negative will be found on the outermost edge of said disc opposite the number on said surface which corresponds to the minimum density lot the negative, a second disc having a radius greater than the smaller radius of the first disc and not greater than the radius of the arc of said circle, said second disc being rotatably mounted about its center concentrically with the first disc and between said first disc and said surface, numbers on said second disc corresponding to the relative sensitivities of different photographic papers, said numbers being arranged on said second disc around an are having a radius less than the minimum radius of said first disc, means for selectively exposing to view only that one of said last-mentioned numbers which corresponds to the sensitivity of the aforementioned indicated paper while maintaining said indicator on said first disc opposite the value of the maximum density of the negative, numbers corresponding to the illumination of the printing light uniformly spaced around part of the edge of said second disc, numbers corresponding to the number of seconds exposure time spaced around a part of the unused portion of said circle and registering with the numbers which correspond to the illumination of the printing light.

2. A calculator for use in determining the proper photographic paper to use and the proper exposure time to be given in order satisfactorily to print from a negative, which comprises a bottom member, density numbers corresponding to the densities of the photographic negatives uniformly spaced around a portion of the arc of a circle on said member, a top disc a portion of which has a radius substantially equal to the radius of said circle and another portion,of which has a radius less than the radius of said circle, said top disc being rotatably mounted about its center concentrically with said circle, an indicator at one point of the outermost edge of said top disc, paper range numbers on said top disc corresponding to the density numbers on said bottom member, said paper range numbers being uniformly spaced from said indicator around the outermost edge of said, top disc and in the same direction as said density numbers but in the reverse order so that when said indicator is set opposite the density number corresponding to one extreme in density of the negative a paper range number indicative of the type of photographic paper that will record the density range of the negative will be found on the outermost edge of said top disc opposite that one of the density numbers which corresponds to the other extreme in density of the negative, an intermediate disc having a radius greater than the smaller radius of the top disc and not greater than the radius of the arc of said circle on the bottom member, said intermediate disc being rotatably mounted, about its center concentrically with the top disc and between said top disc and said bottom member, paper speed numbers on one of said discs corresponding to the relative sensitivities of different photographic papers, said paper speed numbers being arranged around an are having a radius less than the smaller radius of said top disc, means whereby in each one of a number of predetermined positions of the intermediate disc relative to the top disc only one of said paper, speed numbers will be indicated so that when sai dic'ator on the top disc is maintained opposit density number which corresponds to the first mentioned extreme in density of the negative the intermediate disc may be turned relative to the top disc to select that one of said paper speed numbers which corresponds to the sensitivity of the afore-mentioned indicated type of paper that will record the density range of the negative, illumination numbers corresponding to the illumination of the printing light uniformly spaced around part of 3. A calculator for use in determining the proper photographic paper to use and the proper exposure time to be given in order satisfactorily to print from a negative, comprising a bottom member, a series of numbers uniformly spaced around a portion of the arc of a circle on said member, a first disc member concentric with said circle and rotatably mounted relative to the bottom member, a second series of numbers corresponding to said first mentioned numbers and spaced in a like manner around the outermost edge of said disc member, the numbers on one of said members corresponding to the densities of the photographic negatives and forming a density scale and the numbers on the other of said members indicating types of photographic paper and forming a paper range scale, an indicator adjacent one end of the paper range scale whereby when said disc member is turned to bring said indicator opposite a number on said density scale corresponding to one extreme in density of the negative a number indicative of the type of photographic paper that will record the density range of the negative will be found on the paper range scale opposite that one of the numbers on the density scale which corresponds to the other extreme in density of the negative, a second disc member concentric with the first disc member and rotatably mounted relative thereto, the uppermost of the two disc members being cut away along part of its edge to expose an edge por tion of the underlying disc member, paper speed numbers arranged in an arc of a circle on one of said disc members corresponding to the relative sensitivities of photographic papers, means whereby in each one of a number of predetermined positions of said second disc member relative to the first disc member only one of said paper speed numbers will be indicated so that when the bottom member and said first disc member are maintained in the relative position in which said indicator is opposite said number on the density scale which corresponds to the first mentioned extreme in density of the negative the second disc member may be turned to select that one of said paper speed numbers which corresponds to the sensitivity of the aforementioned indicated type of paper that will record the density range of the negative, an additional series of numbers spaced uniformly around a part of the unused portion of said circle on the bottom member, and a second additional series of numbers uniformly spaced around part the edge of said intermediate disc, and exposure time numbers spaced around a part of the un-\ of the edge of said second disc member and adapted to register with said additional numbers on the bottom member, the numbers in one of said additional series corresponding with the exposure time and forming an exposure time scale and the numbers in the other of said additional series corresponding to the illumination of the printing light and forming an illumination scale, whereby when the relative position of said bottom member and said first disc member is maintained as above stated and when the second disc member is turned to select the proper paper speed number for the aforesaid indicated type of paper a number indicating the proper exposure time will be found on the exposure scale opposite that number on the illumination scale which corresponds to the illumination of .the printing light at the printing position.

HARVEY P. ROCKWELL. JR. 

